JMM has had 2 fights above 140 in his entire life, and both of them were catchweights under 147. Technically, he's never fought 'at Welterweight'.

Mayweather, arguably the best boxer on the planet, was his first fight above 140, making the jump from lightweight. And the other fight above 140 was Pacquiao, which he won in my opinion. So what was your point?